U.S. Pat. No. 4,371,752, issued on Feb. 1, 1983 to Matthews et al discloses a voice store and forward system wherein a voice telephone message is digitized, stored and then played back in an analog form to the desired recipient. In order to extend the range of such a system, networks of such systems are utilized which transmit voice messages between the systems on communication channels. These communication channels can be in the form of telephone links such as telephone lines or satellite links.
In effecting an initial connection between two such systems in a network, various forms of addressing are utilized between the two systems to ensure that both are connected together. However, the readiness to receive or transmit data by the telephone systems in the network does not ensure an adequate communication link therebetween for voice transmission. Voice requires a transmission medium having a defined bandwidth in order to adequately reconstitute the voice. The quality of the channel must be sufficient over the entire voice bandwidth, rather than just a portion of it. Since present methods of initiating contact between two systems normally utilize digital transmission or an analog transmission with digital encoded information, the presence of a good digital or analog communication link for purposes of checking a connection does not necessarily ensure a good voice communication link. Therefore, there exists a need for a method of checking the integrity of the channel for voice transmission after a communication link has been effected.